In some conventional brake control apparatuses equipped with a brake-pressure generator for producing a brake force and a pedal-reaction-force generator for producing a pedal reaction force in accordance with the pedal stroke, hysteresis is incorporated in the characteristics of the brake-pressure generator and the characteristics of the pedal-reaction-force generator. By means of such incorporation of hysteresis, the brake force corresponding to the amount of operation of the brake pedal is changed in the direction of applying the brake and in the direction of releasing the brake. Accordingly, brake-pedal sensitivity is reduced to stabilize deceleration, enabling smooth brake operation (see Japanese Patent Application Laid-open No. HEI 11-291894, for example).
Further, one of the proposed brake control apparatuses is capable of shortening the delay in the braking effect in response to abrupt braking by means of the detection of whether or not the brake pedal is abruptly pressed on the basis of a detection signal of a pedal stroke sensor (see Japanese Patent Application Laid-open No. 2000-203402, for example). In this apparatus, when the brake pedal is not abruptly pressed, a target brake force is calculated on the basis of a smoothed value of the detected values of the pedal stroke sensor. When the brake pedal is pressed abruptly, a target brake force is calculated without smoothing the detected values of the pedal stroke sensor. More specifically, the apparatus uses a low-pass filter for averaging the detected values of the pedal stroke sensor when the brake pedal is not pressed abruptly, and turns the low-pass filter off so as not to average the detected values when the brake pedal is pressed abruptly.
However, in the apparatus disclosed in the above Japanese patent HEI 11-291894, although different hystereses are provided for the brake force in the direction of applying the brake and the brake force in the direction of releasing the brake, a brake force is produced with an increasing/decreasing gradient that is determined from a stroke-to-reaction plot for the brake pedal. For this reason, when increasing/decreasing the brake force, a brake force sensitively responsive to the pedal stroke is produced, and thus it is impossible to offer a smooth braking feeling.
Further, in the apparatus disclosed in the above Japanese Patent No. 2000-203402, the low-pass filter is turned off only when the pedal is abruptly pressed. This switching causes the driver to feel uncomfortable. Further, because the determination of whether or not braking is abrupt is based only on the gradient of the pressure applied by depressing the brake pedal. Thus, if pressurization is abrupt, no matter how small the amount of the change in the pressurization is, this leads to abrupt braking. This similarly causes the driver to feel uncomfortable.